1. Field of the Invention
The present invention relates to the augmentation of ventilation and the removal of CO.sub.2 for a medical patient and, more particularly, relates to an apparatus and method for the transtracheal augmentation of ventilation and the CO.sub.2 removal through delivery of a high continuous flow of humidified oxygen and air mixture.
2. Statement of the Problem
As defined by Dorland's Illustrated Medical Dictionary (27th Ed. 1988), ventilation in respiratory physiology is the process of exchange of air between the lungs and the ambient air (i.e., inspiration and expiration).
Three basic approaches are available for assisting or augmenting ventilation for a patient. These can be termed external and closed and open delivery systems.
External negative pressure mechanical devices constitute the first type of system. The Drinker respirator, commonly known as the Iron Lung, assists in pulmonary ventilation over long periods of time by enclosing the patient's body, except the head, in a metal tank. Alternating negative and positive pressures within the tank cause the patient to breathe. Oxygen and air is provided to the lungs and the CO.sub.2 is removed by these pressures. These types of systems are expensive and immobilize the patients. However, they are designed for patients who cannot entirely self-breathe. Such systems also allow a patient to rest their respiratory muscles by having the mechanical systems do the work of breathing.
Under closed delivery systems, a face mask or an endotracheal tube (i.e., inserted through the mouth or nose and into the trachea) is designed to force oxygen under pressure into the lungs of the patient. Closed delivery systems are air tight, separating the lungs of the patient from the atmosphere. Again, oxygen and air is provided to the lungs and CO.sub.2 is removed. Such systems exhibit high inhaling efficiency, but cause irritation or discomfort to the patient through covering of the mouth and nose or through the insertion of a large endotracheal tube into the throat. Closed delivery systems are principally utilized in emergency situations such as intensive care and resuscitation where patients are not able to self-breathe. Such systems are very uncomfortable to patients and are not designed for long term use.
Examples of a closed delivery system are the patents to Jacobs, U.S. Pat. No. 3,788,326 and U.S. Pat. No. 3,682,166 which disclose the use of an occluding balloon to function as a cuff in the throat which minimizes retrograde air leaks during the inflation cycle. This closed delivery system is designed to operate under high pressure (30-100 psi) to physically inflate the lungs.
Open delivery systems supply oxygen into the nostril, the mouth, or the trachea in order to provide oxygen while keeping the lungs of the patient open to the atmosphere. Such systems do not remove CO.sub.2 from the lungs. The CO.sub.2 is removed by the patient's breathing process. These systems are much more comfortable to the patient than closed systems. For example, the patient is usually permitted to speak, eat or drink freely. Open delivery systems are designed for patients who are capable of self-breathing and they are designed for long term use.
Patients generally prefer the use of a transtracheal catheter over the use of nasal prongs for a number of reasons. Complications of nasal prongs include ear sores, serious otitis media, nasal sores, nasal crusting, nose bleeds, diminished sense of smell and taste, tear duct blockage, chronic dry sore throats, hoarseness, and burns caused by ignition of the nasal prongs. Nasal prongs are often removed because of discomfort, restricted mobility or cosmetic concerns. Finally, nasal prongs are unstable and are often dislodged when the patient sleeps.
An example of a transtracheal approach is the inventors' own transtracheal catheter oxygen delivery system trademarked as "SCOOP" which is manufactured by Transtracheal Systems, Inc., 8775 East Orchard Road, Suite 814, Englewood, Colo. 80111. This approach is disclosed in patent applications: 06/883,409 filed June 13, 1986 and 07/101,173 filed Sept. 28, 1987. The "SCOOP" transtracheal catheter uses a high tech biopolymer of 70-90 shore A durometer which resists kinking and crushing. The internal tubing is radiopaque and is available for adults in 9 cm to 11 cm internal lengths. With an inside diameter of 1.7 and 3.0 mm and an outside diameter of 3.5 mm or less, oxygen flow rates up to 6 liters per minute without exceeding the 2 psi back pressure of conventional delivery systems. The SCOOP transtracheal system provides 24 hour oxygen therapy for patients, contributes to a high quality lifestyle, is low cost, provides superior patient mobility, and is comfortable during nocturnal use.
In "Transtracheal Oxygen Decreases Inspired Minute Ventilation" by Couser, Jr. and Make, Am. Rev. Respir. Dis. (1989), the authors further summarized the benefits of the use of transtracheal oxygen (TTO.sub.2) to include: reduction in oxygen requirements, improved compliance, decreased costs, fewer days of hospitalization, improved quality of life, decreased dyspnea, and improved exercise tolerance. The authors investigated the mechanisms for the latter two benefits of decreased dyspnea and improved exercise tolerance by selectively increasing the TTO.sub.2 flow rate from 0.5-1.5, 2, 4, and 6 liters/minute. The authors hypothesized that patients receiving TTO.sub.2 have decreased inspired minute ventilation and inspiratory work of breathing as the mechanism for improved dyspnea and exercise tolerance.
A need therefore exists for an open delivery system exhibiting the above significant therapeutic attributes that functions in the manner of a closed delivery system to provide artificial and augmented ventilation to a patient whose self-breathing is inadequate, nor dependable, to remove CO.sub.2 from the lungs, and to reduce the work of breathing so that the patient's respiratory muscles are not fatigued. A need exists for a long term, home oxygen system that provides nocturnal augmentation of spontaneous ventilation. Furthermore, a need exists for a method of oxygen therapy which improves patient compliance and which can effectively treat some patients who are refractory to nasal cannula delivery.
These needs must be met with a system that does not compromise hemodynamics, that allows for reduction in spontaneous inspired ventilation while maintaining both oxygenation and alveolar ventilation (i.e., elimination of CO.sub.2).
3. Results of a Patentability Search
The results of a patentability search directed towards the teachings of the present invention are set forth below:
______________________________________ U.S. Pat. No. Inventor Title ______________________________________ 3,991,762 Radford Aspirating Device for Patient Ventilation Apparatus 4,520,812 Freitag et al Method and Apparatus for Controlling a Pressure Level In A Respirator 4,569,344 Palmer Aspirating/Ventilating Apparatus and Method 4,593,687 Gray et al Endotracheal Catheter 4,638,539 Palmer Aspirating/Ventilating Apparatus and Method 4,686,974 Sato et al Breath Synchronized Gas-Insufflation Device and Method Therefor 4,805,611 Hodgkins Aspirating Device ______________________________________
An example of transtracheal high frequency jet ventilation (HFJV) is "Method and Apparatus for Controlling a Pressure Level in a Respirator", by Freitag et al., U.S. Pat. No. 4,520,812. Freitag delivers an oscillatory gas stream, at a controlled pressure, from two opposing gas jets through a transtracheal tube. By controlling the pressure and/or frequency of the gas jets, a varying pressure level propagating into the tracheal tube is modulated onto the gas stream. Freitag's apparatus is adjustable within a range of 10 to 1200 pressure pulses per minute with a working pressure between 0.5 to 5 bar.
The patent to Radford, U.S. Pat. No. 3,991,762 entitled "Aspirating Device for Patient Ventilation Apparatus" sets forth a transtracheal catheter used to remove fluid accumulations from the trachea and bronchi of a patient during resuscitation.
The 1986 patent to Gray et al., U.S. Pat. No. 4,593,687 entitled "Endotracheal Catheter" sets forth a method and apparatus for introducing oxygen or a saline solution directly into the trachea in order to facilitate respiration. Gray utilizes a catheter comprising a piece of flexible tubing approximately 1.7 millimeters in diameter and approximately 7.5 centimeters in length with three axially embedded deformed magnetic wires. The distal end of the catheter terminates in an aperture which is smaller in diameter than the inside diameter of the catheter. The proximate end of the catheter terminates in a Leur Lock adapter. The distal end forms a bulbous shape with elliptically shaped slots formed therearound. Insertion of a magnetic probe or stylet causes the bulbous shape to assume a straight and parallel attitude. Under the teachings of Gray, the bulbous shape of the distal end acts to lock or anchor the catheter within the trachea.
The patents to Palmer (U.S. Pat. Nos. 4,638,539 and 4,569,344) relate to an aspirating/ventilating apparatus and method utilizing intensive with a surrounding flexible, collapsible, and preserving film envelope. The Palmer device functions to conjointly ventilate and remove fluid (i.e., aspirate) a patient. Gray utilizes a ventilator that forces air into the lungs of the patient in order to allow the lungs to be adequately expanded and then allows displacement of the air from the patient to be evacuated.
The 1989 patent to Hodgkins, U.S. Pat. No. 4,805,611 and entitled "Aspirating Device" discloses a catheter that is adapted for insertion into the trachea of a patient having at least one aperture for allowing fluid communication between the exterior of the catheter and the passageway contained therein. When the ventilator is used in conjunction with a form of an airway or tube that is inserted into the patient's trachea through the mouth, this is referred to as an endotracheal tube. When a ventilator is used in conjunction with a tube which is inserted into the patient's trachea through an insertion in the patient's neck, this is called a tracheostomy tube. The tracheostomy procedure is preferred because it bypasses and therefore avoids complications of the upper airways. The Hodgkins approach sets forth a tracheostomy tube for removing through suction undesirable secretions from the trachea of a patient.
The 1987 patent to Sato et al., U.S. Pat. No. 4,686,974 sets forth a device and method for insufflating oxygen gas or an anesthetic gas to the respiratory system in synchronism with the patient's breathing. Insufflation of the lungs is the act of blowing air into the lungs for the purpose of artificial respiration. The Sato approach is designed to supply gas only during inhalation periods in synchronism with the breath of the living body in an open type gas insufflation system.
None of the above prior art approaches provide a solution to the problem stated above. None of the approaches uncovered in the patentability search provides an open delivery system which exhibits significant patient comfort, yet functions as a closed delivery system to provide augmented ventilation and CO.sub.2 removal to a patient who cannot fully self-breathe and with long term nocturnal support.
4. Solution to the Problem
The present invention provides a solution to the above-identified needs by utilizing a small diameter transtracheal catheter such as the inventors' "SCOOP" transtracheal catheter and by delivering a high continuous flow (HCF) of an oxygen/air mixture at controlled pressure, humidity, and temperature on a continuous basis into the lungs of a patient with inadequate breathing to augment ventilation and to facilitate the removal of CO.sub.2.
The present invention is designed as a long term, home oxygen system that provides for nocturnal augmentation of spontaneous ventilation. The present invention also offers a choice for patients who have inadequate breathing due to respiratory failure resulting from problems with shortness of breath, CO.sub.2 removal, and respiratory muscle strength.
The present invention may also be used in an intensive-care unit for hospitalized patients requiring augmentation of spontaneous ventilation. The invention may particularly be advantageous for patents requiring long term stays in intensive care.
While the present invention permits nocturnal augmentation, oxygenation and alveolar ventilation is maintained even though spontaneous inspired ventilation decreases. This is important for patients who cannot fully self-breathe as it allows for the patient's breathing muscles to relax and to become rested. In other words, the present invention provides respiration through high volume continuous flow through the lungs without forcing pulses of high pressure air into the lungs to simulate breathing as in closed delivery systems or through the use of alternating positive and negative air pressure external to the body in order to simulate breathing as found in iron lungs.
The present invention is also useful for patients suffering from sleep apnea, which is a condition causing transient attacks of obstruction of the throat and/or failure of automatic control of respiration, resulting in alveolar hypoventilation. This condition becomes more pronounced during sleep. Nocturnal use of the present invention is an aid against sleep apnea.
Finally, the present invention has a further advantage for those patients who are capable of some sustained self-breathing in that the same transtracheal catheter may be used for day time use in a standard transtracheal oxygen supply system when the patient is capable of self-breathing and for nocturnal use in the system of the present invention when the patient has respiratory failure, retention of CO.sub.2 , and/or the inability to sustain the work of breathing.